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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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As there is no data available for tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate ("PBTCNa4"), results of the parent acid, 2-phosphonobutane-1,2,4-tricarboxylic acid ("PCBT") are taken into account for this endpoint.
PBTC as sole source of carbon, both with PBTC and orthophosphate as sources of phosphorus, is not biodegradable by enrichment cultures from river water and river sediment but by certain strains gained from these cultures. PBTC is also biodegradable by enrichment cultures from river water and river sediment if an alternative source of carbon is available, even if inorganic phosphate is present (in sub-ppm range). Both (alternative carbon source, inorganic phosphate) are present in many environmental surface water. The biodegradation is more effective and faster if a certain strain or strain combination gained from this both ecosystems was used. Slow degradation under anaerobic conditions for cultures from rivers sediment and river water is not clearly stated by the publication but can be strongly be assumed based on the presented information. In conclusion, PBTC is biodegradable under environmental conditions. Abiotic degradation was not observed.

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Additional information

As there is no data available for tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate a read-across approach with 2-phosphonobutane-1,2,4-tricarboxylic acid disodium salt is proposed. In aqueous media, both substances dissociate into the corresponding anion (2-phosphonatobutane-tricarboxylate ion) and the sodium ion and hydrogen ion (proton), respectively. Fate, behavior and the ecotoxicological properties of both substances are thought to be an effect of the phosphonato-carboxylate ion rather than of the sodium ion or the hydrogen ion (proton), which are normal constituents in environmental systems and have no relevant ecotoxic properties in low concentrations. Therefore a read-across between tetrasodium hydrogen 2-phosphonatobutane-tricarboxylate and 2-phosphono-butane-1,2,4-tricarboxylic acid disodium salt is justified.

Opposed to OECD guideline 308, not a water-sediment system but the inocula gained from river water and river sediment were separately tested for their ability to degrade 2-phosphonobutane-1,2,4-tricarboxylic acid ("PBTC"). The test material PBTC was used as recrystallised disodium salt. PBTC as sole source of carbon, both with PBTC and orthophosphate as sources of phosphorus, was found to be not biodegradable by enrichment cultures from river water and river sediment. Biodegradability was found either by certain strains gained from these cultures or if an alternative source of carbon is available. In the latter case degradation was observed, even if in the presence if inorganic phosphate. Both (alternative carbon source, inorganic phosphate) are present in many environmental surface water. Thus, PBTC is biodegradable under environmental conditions equivalent / similar to the test conditions.
The biodegradation was shown to be more effective and faster if a certain strain or strain combination gained from this both ecosystems was used.
Slow degradation under anaerobic conditions for cultures from rivers sediment and river water is not clearly stated, but was strongly assumed, based on the presented information. Abiotic degradation was not observed.

The study has shown that biodegradation of PBTC in river water and river sediment under environmental conditions primarily depends on the presence of an alternative carbon source and could be optimized certain strains that can easily be enriched and isolated from these both compartments.